Driver for recessed head fasteners



Feb 1966 G. B. STILLWAGON, JR 3,

DRIVER FOR RECESSED HEAD FASTENERS Filed June 24, 1963 INVENTOR.

GEORGE B. STILLWAGON,JR.

AT TORN EYS United States Patent Ofitice Patented Feb. 15, 1966 3,234,982 DRIVER FQR RECESSED HEAD FASTEi ERS eorge B. Stillwagon, J12, Dayton, Ohio, assigner to Gardner-Denver Company, Dayton, Ohio, a corporation of Delaware Filed June 24, 1963, Ser. No. 289,996 Claims. (Cl. 145-50) This application relates to drivers, such as bits and the like for recessed head fasteners.

Recessed head threaded fastener devices have become generally used throughout the industry in manufacturing and assembling operations since they are readily adapted for use with power driving devices. However, the bits used with such power driving devices often break long before they are worn out. Such breakage may occur at one of the driving wings of the tool or it may occur completely across the lower or small end of the tool. It has been found that such breakage is the result of either concentration of the driving load at any one or two of the driving wings, or a concentration of torque at the tip of the bit rather than further up on the wings.

It has accordingly been found that the tip of the bit is the point which is most vulnerable to breaking and, at the same time, has the poorest driving efiiciency in that it provides the least amount of driving leverage and s tear strength. One of the important objects and advantages of this invention is the provision of a tool for driving recessed threaded fasteners which is configured so that the driving contact of the wings is concentrated at an area of highest strength of the bit, which is also the area of greatest mechanical advantage. A further advantage which accrues is that the driving force is applied to the threaded fastener head at a region of its greatest strength.

The above object and advantages of this invention are achieved by suitably forming, such as by milling, coining, or relieving, the driving wings so that driving contact between the wings and the adjacent driven surface of the recess is limited to a region adjacent the top or the outer surface of the screw recess. Stated another way, the invention provides a bit which has wings configured such that the major portion of the torque is applied to the screw recess by the portion of the driving wings nearest the top opening of the recess. In this manner, the invention assures that none of the driving torque is applied to the threaded fasteners through the tip of the bit or through the portion of the wings nearest the tip, when properly entered in the recess.

It is therefore a further object of this invention to provide a driving tool which is characterized by less frequent breakage and increased useful life.

A further object of this invention is to provide a more eflicient driving tool for cruciform-slotted fasteners.

A still further object of this invention is to provide a driver having relieved wings which provides easy entry into the slot and which assures that the driving torque is transmitted through the Wings adjacent the top of the screw recess.

A further object of the invention is to provide an improved driving bit of the character described for use with screw slots having a negative lead angle on the driving side and which does not materially increase the cam out between the driver and the driven elements.

These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings:

FIG. 1 is an elevation of a driver constructed according to this invention shown as being received in the head of a typical threaded fastener shown in section;

FIG. 2 is a horizontal section through the driver and fastener taken generally along the line 2-2 of FIG. 1 showing the driving contact between the wings and the driven recess surfaces;

FIG. 3 is a further horizontal section taken generally along the line 3-3 of FIG. 1 showing the relief of the driving wings and the absence of driving contact;

FIG. 4 is a section similar to that of FIG. 3- but taken further down in the recess toward the tip of the driver generally along the line 4-4 of FIG. 1;

FIG. 5 is an enlarged fragmentary elevational view of one of the driving wings of the driver of FIG. 1;

FIG. 6 shows a modified form of the wing of FIG. 5;

FIG. 7 is an elevational view of a modified form of the invention particularly adapted for use with screw recesses having a positive lead angle or undercut formed in the driven surface of the slot;

FIG. 8 is a partially broken away elcvational view of the head of a threaded fastener having such an undercut;

FIG. 9 is a partially broken away elevational view showing the driver tool of FIG. 7 inserted in the socket of FIG. 8;

FIG. 10 is a transverse section taken generally along the line 1010 of FIG. 9; and

FIG. 11 is an enlarged elevational view of one of the driving wings of the embodiment of FIGS. 7-10.

Referring to the figures of the drawing which illustrates preferred embodiments of the invention, a driver tool or hit for driving screw threaded fasteners is shown at in FIG. 1. The bit 20 may have an upper end adapted for attachment to a driving handle, but is preferably formed in such a manner as to be received within a suitable chuck or bit holder on a power tool. The material of the body of the tool 20 may be constructed from stock material such as from a length of hexagonal bar stock which has had the driving end tapered toward a point. While cylindrical stock may be used, 'the hexagonal or other flat-sided stock material is preferred since it provides a secure mounting for use with power tools and the like.

The driving end of the bit 2a) is formed with a plurality of equally spaced driving blades or wings 22 which are separated by flutes 23. The wings 22 can he formed initially by milling material from the body of the tool to form the fiutes 23 between the wings, or they may also be formed by any other suitable machining or forming operation, such as coining, grinding and the like. The outer surfaces 25 of each of the wings 20 decrease in radial height from the shank of the bit 2-? toward the lower end or tip 26, due to the previously-mentioned taper.

Each of the wings 22 is formed with a driving face or surface on one side thereof for engagement with the driven surface 32 of the cruciform-slot or recess 33 of a threaded fastener 34. The slot 33 may be of the common Phillips type as shown in the patent to Phillips 2,046,839 of 1936, which has substantially symmetrically wing receiving slots.

The bit 20 of FIGS. l5 is provided with means for confining the major portion of the driving torque to the portion of the wings 22 in the slots 33 adjacent the upper surface 35 of the screw head 35. The means of this embodiment may be seen at FIG. 5 as including a relief 4which is formed in the driving face 30 over the lower axial portion thereof adjacent the tip 26 and preferably uniform over the axial extent thereof, leaving an unrelieved driving zone 42 which conforms to the adjacent driven face 32 of the recess 33 at the region of greatest diameter of the head 36, which is also the region of great est strength and radial dimension of the driving wings The relief may be formed by grinding, coining,

or any other suitable process and need only have a depth in the order of a few thousands of an inch. The vertical or xial extent of relief 49 on the wings 22 may vary within e lii..'ts, but peferably it extends between fifty and cignty percent of the effective axial extent of the wings 22, leaving a driving zone 42 of from twenty to fifty percent of the effective axial extent of the wings 22 within the scr w slots 33.

The section of FIG. 2 is taken through the zone 42 and shows the driving contact between the driving surface 36* of the wings 22 and the driven faces 32 of the head 3-5. Similarly, the sections of FIGS. 3 and 4 are taken through the portions of the wings forming the relief 43 and show, in slightly exaggerated form, a clearance space 59 between the wings 22 and the face 32 and a lack of effective driving contact throughout the relief zone 4t It will therefore be seen that the relief assures that the driving contact between the wings 22 and the adjacent driven surfaces 32 of the recess 33 is confined to the regions nearest the upper surface 35. This is the region of the greatest mass and strength of the screw head. it is also the region of greatest radii and accordingly provides the most etlicient drive connection for the transmission of torque, and it is the region of greatest strength in the wings 22. In addition, the flutes are relieved to form a clearance 23 (FIGS. 2, 3) to confine the driving of the wings.

The modification shown in FIG. 6 is one in which a relief 4% has been formed on both the driving and the reverse driving faces of a wing 22. This embodiment may be of advantage where the tool is to be used for both driving and removing, or where it is more convenient to form the relief 42') uniformly throughout the radial epth of the wings in the walls forming the flutes 23.

The embodiment of the invention shown in FIGS. 7-11 is particularly adapted for use with recesses which are formed with an undercut or a positive lead angle on the driving face. One such recess is shown in enlarged detail in FIG. 8 in which the driving face 68 of the slot 61 is undercut at a lead angle 62. The reverse driving face 64 of the slot 61 may be provided with a normal negative lead angle 65, as shown in United States Patents 2,800,829 and 2,592,462.

Referring to FIG. 7, it can be seen that the bit 70 is formed with four generally equally spaced driving wings 72 separated by smoothly curved flutes 73, which flutes each form a clearance space 72 with the screw slot (FIG. 10). The bit 70 also includes relief means formed on the driving face of each of the wings 72 for limiting the driving contact to regions adjacent the top of the slots 61 and defining a clearance space 76 (FIG. 9) between an inner portion of the wings and the adjacent surface of slot 61. In this embodiment, the relief on the driving face 75 of the wings 72 takes the form of either an axially strai it or slightly negative lead angle 80, as shown in exaggerated form in FIG. 11. The relief which is ac cordingly formed in each of the driving faces 75 of the wings 72 is more prominent near the tip 81 of the bit than at locations which are axially remote from the tip for confining the driving contact of the driving surfaces or faces 75 to regions of the greatest radial dimensions of the wings within the fastener recess.

As an example and without limiting the scum of the invention herein, undercut angle 62 of the slotted recess be the order of onehalf to one degree, and the lead angle 86 on the driving wing may be in the order of Zero to one degree. The effective relief formed thereby is sufficient when used with undercut screw recesses to assure that the major portion of the driving contact is connned to the area of the screw recess adjacent the upper surface S2 of the fastener. The invention also has the advantage of permitting easy entry into the screw recess and easy removal at the conclusion of the driving, as us better initial fit without experiencing sticking of 4- tlte bit in the recess after the screw fastener is driven, especially when impact type tooling is used.

It has been found that drivers having wings formed with a positive lead angle for full conformance with such screw recesses are not only subjected to loads and moments at the tip of the bit tending to break the bit, but also tend to be selfloclring into place, with the result that the bit often hangs up in the recess when the power tool is withdrawn.

The embodiment of FIGS. 7-11 does not hang up. Also it does not i the effect of increasing the cam out since the total diffcrenence in angle between the driving surface of the wing 72 and the driven face 69 may be in the order of one degree, and the component of force tending to cause the bit to slip out of the recess is considerably less than the coeificient of friction between the bit and the walls of the recess. Also, as shown in FIG. 9, the wings 72 are configured at the reverse driving surfaces for confining contact to the regions that are closely adiacent the common point or tip 81 of the bit, as shown at 95 in FIG. 9, to provide stability of the bit within the recess.

A further advantage of the construction of the bit of FIG. 7 resides in the fact that the recesses in screw eads are formed by punches. When the punch enters the material of the screw head there results a falling away of the material of the screw head and when it leaves the recess, it is not always possible in production to assure that an undercut does, in fact, exist .in the recess. Drivers having similarly undercut driving wings when used in such recesses drive at the bottoms of the wings. The relief formed on the driving wings of the bit 70, assures that the driving force is confined on the wings at the areas of greatest strength, over a wide variation in screw recesses between the achievement of an actual undercut and recesses in which this is not fully achieved.

It is within the scope of this invention to apply the technique of a relief 80 on the driving surface of the wings to the embodiment of FIG. 1, for use with screws having ordinary cruciform recesses. Also, it is within the scope of this invention to employ the relief 40 of the embodiment of FIG. 1 with the fasteners having the undercut recesses such as shown in FIGS. 8 and 9. It will therefore be seen that this invention provides driver bits formed with a relief at least on the driving surfaces of the wings, with the relief being more prominent near the tip of the bits than at locations axially removed from the tip for confining the driving contact of the wings to regions axially remote from the tips. This assures that the major portion of the driving contact is confined to the region of greatest radial wing diameter and greatest strength adjacent the head or upper surface of the slotted recess, thereby reducing breakage due to loading at the tip of the bit while providing for easy entry and removal.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing rom the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A driver tool adapted for driving screw threaded fasteners characterized by a cruciform-slot, comprising a body, a plurality of driving wings on said body extending axially from a tip of said body separated by flutes, each of said wings having a driving surface formed on one face thereof and extending generally uniformly radially thereof, arTd relief means formed in each of said wings on said driving face between an axially inner portion of each of said wings adjacent said tip and the adjacent driven surface of such a fastener slot confining driving contact to an axial region on said wings remote from said tip.

2. A driver tool adapted for driving screw threaded fasteners characterized by a cruciform slot, comprising a body, a plurality of generally comically tapered driving wings on said body-separated by flutes extending axially of said body and terminating in a tip, each of said wings having a driving surface formed on one face thereof ex-- tending generally uniformly radially thereof, and means in each of said wings at said driving surface forming a relief adjacent said tip and positioned axially inwardly of the top of such a fastener slot limiting driving contact of each of said wings to a region of greatest radial diameter of said wings within the screw slot.

3. A driver tool adapted for driving screw threaded fasteners characterized by a cruciform recess comprising a driver body, a plurality of driving wings on said body terminating in a tip and separated from each other by flutes, each of said wings having a driving surface formed on one face thereof and extending generally uniformly radially thereof, and means on each of said wings defining a relief on each of said faces which is more prominent near said tip of said bit than at locations axially removed from said tip for confining the driving contact of said wngs with such a recess to regions axially spaced from said tip.

4. A driver bit for use with power tools adapted for driving screw threaded fasteners characterized by a cruciform recess comprising a driver body, a plurality of equally spaced driving wings in said body extending axially and terminating in a common tip, each of said wings having a forward driving surface and a reverse driving surface formed on opposite faces thereof, and means on each of said wings forming a relief in each of said forward driving surfaces with said relief being more prominent near the tip of said bit than at locations axially removed from said tip for confining the driving contacts of said forward driving surfaces to regions on said wings which are axially spaced from said bit tip.

5. A bit for use with power tools and the like adapted for driving threaded fastencrshaving a cruciform driving recess, comprising a bit body, means on said body defining a plurality of generally equally spaced driving wings extending axially thereof and terminating in a common bit point, each of said wings having a forward driving surfacev on one face thereof and a reverse driving surface formed on the opposite face thereof, means on each of said wings forming a relief in said forward driving surfaces with said relief being more prominent near the said common point of said wings than at locations which are axially spaced from said point for confining the driving contacts of said forward driving surfaces to regions on said wings which are axially spaced from said common point, and said wings being further configured at said reverse driving surfaces confining contact of said reverse surfaces to regions closely adjacent said bit common point providing stability of the bit within such recess.

References Cited by the Examiner f UNITED STATES PATENTS 2,800,829 7/1957 West.

WILLIAM FELDMAN, Primary Examiner.

MILTON S. MEHR, Examiner. 

1. A DRIVER TOOL ADAPTED FOR DRIVING SCREW THREADED FASTENERS CHARACTERIZED BY A CRUCIFROM-SLOT, COMPRISING A BODY, A PLURALITY OF DRIVING WINGS ON SAID BODY EXTENDING AXIALLY FROM A TIP OF SAID BODY SEPARATED BY FLUTES, EACH OF SAID WINGS HAVING A DRIVING SURFACE FORMED ON ONE FACE THEREOF AND EXTENDING GENERALLY UNIFORMLY RADIALLY THEREOF, AND RELIEF MEANS FORMED IN EACH OF SAID WINGS ON SAID DRIVING FACE BETWEEN AN AXIALLY INNER PORTION OF EACH OF SAID WINDG ADJACENT SAID TIP AND THE ADJACENT DRIVEN SURFACE OF SUCH A FASTENER SLOT CONFINING DRIVING CONTACT TO AN AXIAL REGION ON SAID WINGS REMOTE FROM SAID TIP. 